This invention relates generally to the fabrication of semiconductor devices, and more particularly to the fabrication and encapsulation of semiconductor devices using a composite mold with selectable inserts.
Semiconductor devices are often encapsulated in a protective plastic body from which a plurality of leads extend to allow electrical contact and interconnection with the encapsulated semiconductor device itself. The protective plastic body is formed by injecting plastic into a mold which surrounds each of a plurality of individual devices and associated leads. The molds which are used to form the plastic packages are very expensive to produce, in part because they must be machined from extremely hard materials such as tool steels, tungsten carbides, and the like. Additionally, the molds themselves are difficult to machine, including very small details which must be precisely implemented. The extremely hard materials are necessary to withstand the abrasive quality of the plastic encapsulating materials. Even the hard materials used for the molds, however, show signs of wear after repeated molding operations. This wear is especially severe along the gates through which the plastic flows as it passes from a source of supply to the individual device sites.
The expense of making the molds argues against proliferation of mold types and also against experimenting with new designs. Despite this, the need for new and complex package types and for expensive new molds to fabricate each of the new packages is ever increasing. As the complexity of the semiconductor device increases, the number of leads necessary for contact and interconnection increases. With the very complex integrated circuit functions presently being implemented in a single packaged device, the number of leads has increased to tens and even hundreds of leads on each device package. The many device leads must be maintained in precise shape, position, and alignment so that the packaged device can be reliably affixed to a printed circuit board or other application. During testing, handling, and other operations there is a high probability that one or more of the large plurality of leads will become bent, misaligned, or moved out of planarity with the other leads. One solution to this problem has been to use a molded carrier ring with the device. A molded carrier ring is a protective ring surrounding and spaced apart from the package body which is molded around and supports the ends of the leads while providing means for contacting those leads for testing and the like. After the testing and most of the handling has been completed, the molded ring is excised from the lead frame and the leads are cut and formed to their desired, finished form. This cutting and shaping is done at a point in time that is close to the time when the device will actually be placed in operation so that little additional handling must be done. The possibility of misaligning the leads is therefore significantly reduced and the yield to the assembly operation is appreciably enhanced.
The semiconductor industry is beginning to standardize on a limited number of carrier ring configurations. A large number of package types will be accommodated with a limited and much smaller number of ring configurations. A variety of different packages will use the same ring configuration so that a large proliferation of handling equipment will be avoided. This means that a limited number of handler, tester, and other equipment variations are needed to accommodate a large number of package types.
As the concept of molded carrier rings spreads through the industry and replaces a number of existing, non-carrier ring configurations, and as new applications arise, new molds must be generated for each of the new package types and to replace those molds which have excessive wear. This is a very expensive and time consuming endeavor. A need existed, therefore, for a method for fabricating semiconductor devices and especially for the packaging thereof in carrier ring configurations which would reduce the cost of the molding operation, would provide flexibility, and would reduce the cycle time for implementing new package designs.
It is therefore an object of this invention to provide an improved process for the fabrication of semiconductor devices.
It is another object of this invention to provide an improved process for the fabrication and packaging of semiconductor devices in a carrier ring configuration.
It is yet another object of this invention to provide an improved process for fabricating semiconductor devices which allows for the changing of design or for the refurbishing of mold gates.
It is a still further object of this invention to provide an improved and flexible method for the fabrication and encapsulation of semiconductor devices.